With the increasing emphasis on packages, mail, and other such items having to arrive “overnight”, more and more cargo is being shipped by aircraft 100 (See FIG. 1). While some aircraft are configured to transport cargo only (so called, “freighters”), others are configured to transport both passengers and cargo.
Typically, the items being shipped are first loaded onto pallets, containers, or the like. In the airfreight industry, any one of these various categories of devices is referred to as a Unit Load Device 102 (ULD). Within each category, the ULDs come in various sizes, shapes and capacities and bear markings that identify their type, maximum gross weight and tare weight, among other characteristics.
This initial task of placing the items to be shipped into a ULD may be performed at a location away from the immediate vicinity of the aircraft. In due course, however, the ULD is weighed, brought to the aircraft and sent up a ramp 106, scissors lift, or other means and then through a doorway 108. Once inside, the ULD is moved about the cargo compartment until it reaches its final position for the flight. As depicted in FIG. 2, on any given flight, a cargo aircraft 200 can carry a number of ULDs 202, of which aforementioned ULD 102 may be just one example, and so additional ULDs are brought onboard and placed in their proper positions. In certain aircraft, not all ULDs are in the same compartment, some being placed in the forward compartment 204 while others being placed in the aft compartment 206. And, as seen in the forward compartment 204, even ULDs of the same type need not necessarily all be adjacent to one another. Also, in many aircraft, ULDs may be placed on different vertical levels, or decks.
To facilitate moving around the ULD within the cargo compartment, the floor of the cargo compartment is provided with a number of structures with raised surfaces. These structures may take the form of parallel roller tracks arranged longitudinally along the length of the cargo floor, ball panel units, and the like. The bottom surface of the ULD rides on the raised surfaces provided by the rollers and balls of these structures, as it is moved within the compartment.
Once moved to its final position, further movement of the ULD is prevented for duration of the flight. This is done to ensure that the ULD will not move about when the aircraft is subjected to rough air, vibrations, acceleration, deceleration, and rough landings. To prevent movement of the ULD in flight, the floor and side walls of the cargo compartment may be provided with restraints that serve to keep the ULD stationary.
The number of ULDs, the types of ULDs to be carried, and the weight of each ULD can change from flight to flight. Great care must be taken when loading aircraft with cargo to assure that the weight and balance of the aircraft with the loaded cargo is acceptable. In part, this is because an aircraft can be damaged while sitting on the ground if the cargo weight distribution is incorrect, causing the aircraft to “tip” onto its tail. And in flight, aircraft performance and handling characteristics are affected by the gross weight and center of gravity limits. An overloaded or improperly balanced aircraft will require more power and greater fuel consumption to maintain flight, and the stability and controllability may be seriously affected. Lack of appreciation for the effects of weight and balance on the performance of aircraft, particularly in combination with such performance reducing factors as high density altitude, frost or ice on the wings, low engine power, severe or uncoordinated maneuvers, and emergency situations, can be a prime factor in aircraft accidents.
Before the ULDs are loaded, the load master, or other cognizant individual, develops a pre-planned load configuration that takes into account the weight and balance criteria, and the number, types and weights of the ULDs. This pre-planned load configuration indicates where, on the cargo floor, each of the ULDs to be loaded onto the aircraft, should be positioned. In its simplest form, then, the pre-planned load configuration is simply a two-column list, the first column identifying each ULD and the second its corresponding desired final location within the aircraft. In general, however, the pre-planned load configuration is part of a more comprehensive cargo loading manifest that may also include information about the weight of each ULD, among other items. The loading crew tasked with loading the aircraft receives a print out of the pre-planned load configuration, and loads the cargo hold accordingly.
However, a typical main deck freighter aircraft can have hundreds of permutations for cargo loading configurations. For this reason, it can be a difficult task to ensure that the ground crew has loaded the aircraft correctly for an intended load. It is therefore desirable to provide real time weight and location of all of the loaded cargo to calculate the weight and balance of the aircraft, as well as to track the cargo while loading the aircraft and later at the conclusion of the flight while the cargo is being unloaded.
The prior art includes RFID tags and RFID readers. A tag may be placed on an item and later scanned by an RFID reader, thereby tracking that item. Wireless systems, such as those provided by Wherenet (www.wherenet.com) may be used to track and locate objects in a variety of settings.